The Long Term Evolution (LTE) wireless communication technology includes an advancement known as LTE-U (LTE-Unlicensed), also referred to as LAA-LTE (Licensed Assisted Access-LTE), that utilizes unlicensed spectrum, typically in the 5 GHz band to provide additional radio spectrum.
Channel access mechanisms over the uplink channel are needed when LTE is deployed with Listen-Before-Talk (LBT) over unlicensed spectrum (e.g., via LAA). Due to LBT employed at both an Evolved Node B (eNB or eNodeB) and User Equipment (UE), existing LTE uplink scheduling with synchronous Hybrid Automatic Repeat Request (HARQ) schemes does not work.